1. Field of the Invention
The invention is directed to an ophthalmic device and an arrangement for generating images with expanded dynamic range and to a corresponding method for generating images with expanded dynamic range.
2. Description of Related Art
In the following, the expression ‘radiant energy’ is understood to mean not the energy of individual photons, but rather the total energy of all photons which is integrated over an exposure time.
The dynamic range of an image indicates the ratio of the highest intensity and lowest intensity contained in the image. When making a photographic recording of an object, either a short exposure time (low radiant energy) must be selected for discernible imaging of bright areas without saturation effects (to prevent overexposure) or a long exposure time (high radiant energy) must be selected in order to image dark areas with sufficient contrast (to prevent underexposure). The other areas are then necessarily underexposed or overexposed in the recorded image. In both cases, the dynamic range is low. A known solution to this problem is to record two or more images of the same object successively with different exposure times. The bright areas of the object and the dark areas of the object are then discernible to varying degrees in the different images. These different images must be viewed in parallel in order to perceive all of the information.
Numerous methods are known in the art for combining a plurality of photographic images of low dynamic range, particularly digital photographs, to form an individual image with an expanded dynamic range. Bright areas and dark areas can then be perceived simultaneously in the combined image with expanded dynamic range.
Particularly in ophthalmology when imaging segments of the eye, weakly reflective structures and highly reflective structures occur at close distances from one another. For a more accurate diagnosis, all of the structures must be imaged as distinctly as possible, preferably within an individual image with a high dynamic range so as to perceive all of the structures simultaneously. However, sequential imaging with different exposure times on the eye is unacceptable for two reasons. First, the eye is constantly in motion, which typically results in the eye being recorded in different positions. An individual image with expanded dynamic range can be compiled from different individual recordings of this kind only with great effort. Second, a repeated exposure with the necessary intensive illumination means, in effect, a longer exposure and, therefore, a larger dose of energy deposited in the eye because a large proportion of the light falling on the eye is absorbed in the eye. However, the deposition of energy should be kept as small as possible in order to minimize the risk of damage to health.